Fouling of petroleum processing equipment occurs continuously during the period when petroleum or its derivatives are being processed in the equipment. Generally, fouling is caused by the gradual buildup of a layer of polymeric material resulting from the thermal polymerization of unsaturated materials which are present in the material processed. Gaseous materials are frequently scrubbed to remove undesired components. Hydrogen sulfide and other impurities are commonly removed from gas streams by scrubbing with an alkanolamine composition. That operation leads to formation of iron sulfides creating an additional fouling problem. Ultimately fouling becomes a problem of such magnitude that it becomes necessary to take the equipment out of service for cleaning. Cleaning is an expensive, time consuming operation and consequently methods of preventing fouling, or at least significantly reducing the rate of fouling, are constantly being sought. The most economical method of reducing the fouling rate in process equipment is to add chemicals which inhibit fouling, called "antifoulants", to the feed stream being processed.